This invention relates to a method of manufacturing a semiconductor light emitting device, a semiconductor light emitting device, method of manufacturing a semiconductor device, a semiconductor device, a method of manufacturing a device, and a device itself, that are suitable for use in the manufacture of semiconductor lasers, light emitting diodes or electron transport devices composed of nitride III-V compound semiconductors, for example.
Widely used conventional methods for manufacturing semiconductor devices first grow desired semiconductor layers on appropriate substrates and then treat the layers. In general, semiconductor layers are liable to change in properties, very sensitively following information on substrates, such as their lattice constants. Therefore, it will be the best way to use substrates that are homogeneous to desired semiconductor layers and to grow thereon the semiconductor layers by epitaxial growth.
Therefore, substrates of semiconductor devices should preferably be made of materials that are common in nature to semiconductors used in devices and have low densities of dislocations or other defects. This is because defects of substrates are copied to semiconductor layers growing thereon and often invite deterioration of device properties.
Nitride III-V compound semiconductors represented by GaN have large band gaps. For this advantage, they are under progressive development in form of light emitting elements for wavelength ranges from ultraviolet to violet, blue and green, which are difficult to obtain with other semiconductors. Actually, light emitting diodes (LEDs) and semiconductor lasers (LDs) using nitride III-V compound semiconductors have been brought into practice.
However, nitride III-V compound semiconductors are difficult to form by bulk growth, and it has been difficult to obtain substrates reduced in defect to a level acceptable for use as substrates of semiconductor devices. Therefore, in almost all cases, nitride III-V compound semiconductors must be formed by crystalline growth on substrates of sapphire, SiC, or the like, that are different in nature from the nitride III-V compound semiconductors to be grown, and the process of forming low-temperature buffer layers is required. However, even through that process, nitride III-V compound semiconductors obtained by growth exhibit very high defect densities, and give considerable influences to device properties.
Under the circumstances, there is a demand for a substrate of the same quality, that is, made of a nitride III-V compound semiconductor, and having a reduced density of defects, which is suitable for use as a substrate for manufacturing a nitride III-V compound semiconductor device having improved properties.
Heretofore, JP-2001-102307 has proposed a method of manufacturing a single-crystal GaN substrate as a method of manufacturing a nitride III-V compound semiconductor substrate having a reduced density of defects. This method intends to reduce dislocations by controlling the growth surface of vapor-phase deposition to have a three-dimensional facet structure instead of a flat state and progressing growth while keeping the facet structure and not burying the facet structure.
However, the technique disclosed by JP-2001-102307 concentrates breakthrough dislocations especially to certain regions of the growth layer and thereby reduces breakthrough dislocations of the other regions. Therefore, the single-crystal GaN substrate locally includes low defect density regions and high defect density regions. Moreover, it is out of control where the high defect density regions appear, and they appear at random. Therefore, in case a semiconductor device, such as a semiconductor laser, is manufactured by growth of nitride III-V compound semiconductor layers on the single-crystal GaN substrate, this technique cannot prevent a high defect density region from being formed in the emission region, and inevitably invites degradation of emission properties and reliability of semiconductor lasers.
It is therefore an object of the invention to provide a semiconductor light emitting device excellent in property such as emission property, reliable and elongated in lifetime, as well as a method capable of manufacturing such a semiconductor light emitting device.
More broadly, an object of the invention is to provide a semiconductor device improved in property, reliable and elongated in lifetime, as well as a method capable of manufacturing such a semiconductor device.
Still more broadly, an object of the invention is to provide various types of devices excellent in property, reliable and elongated in lifetime, as well as a method capable of manufacturing such devices.